Automatic speed stabilizing device for aircraft



March 8, 1938. E. 'Fxscl-'IEL 2,110,622

' AUTOMATIC SPEED STABILIZ-ING DEVICE FOR AIRCRAFT Filed March 7, 1935 f,ff 7

Passed s, 193s AUTOMATIC SPEED FOR s'rABnJzmG DEVICE amenan- EduardFischel, Berlin-Charlottenburg, Germany, assigner to Maschinen G. m. b.H., Berlin, Germany, a corrmany poration of Ge Applicati? March '7,

Siemens Apparate und 1935, Serial No. 9,820

Germany March 7. 1934 13 Claima My invention relates to automatic speedstabilizing devices for aircraft, and more particularly for airplanes.

Speed stabilizing devices for aircraft in which the relative speed ofilight is maintained constant by the automatic adjustment of theelevator in accordance with the departures of the relative wind speedfrom a desired speed to be maintained constant are well known. En thiscase the dynamic pressure oi the relative wind acts, as a rule, on adiaphragm which is subjected to a counter-tension proportional to thedesired speed of night. The deections ci the diaphragm are thentransmitted to the elevator by means of a correspondingly controlledservo-mechanism so that the control stick is pushed forward, if therelative speed of flight is too small, whereas it is pulled back if therelative speed oi night is too great.

The invention has for its object to provide a device for automaticallystabilizing the absolute speed of flight, that is to say, the speedrelative te ground ci airplanes which may differ considerably from therelative speed of night depending upon the force and the direction ofthe wind relative to the direction of course. The maintenance of theabsolute speed oi flight relative to ground to a constant value may bevery desirable in many cases, particularly if commercial airplanes areto travel according to a certain sched- Jie of times. The stabilizationoi the absolute speed of iiight may be accomplished according to theinvention by the elevator controlof the airplane, for instance, byaservo-mechanism which adjusts the elevator, being automaticallyregulable in accordance with the deections oi' a measuring device forthe speed of ilight relative to ground. n'this case the regulation isonly possible within certain limits determined by a relative windspeedometer. This is necessary in order to ensure the maintenance of therelative speed required for the minimum lift of the alrplane at aconstant value, in such cases in which the airplane is aected by astrong wind blowing in the direction of ilig t.

To avoid great changes o1' altitude or the airplane with the abovestabilization of speed'caused by the adiustment of the elevator controlit is preferable to bring about simultaneously with this control anautomatic stabilization of altitude by controlling the propelling forceof the airplane in accordance with the departures from the desiredaltitude. This may be effected automatically in a manner well known inthe art by controlling the supply of gas to the driving motors of theairplaneV by means of an altimeter which is set for the desiredaltitude, for instance, with the aid oi a servo-mechanism. `Furtherdetails of the invention, particularly lalso-the device serving tomeasure the speed oi s ight relativeto ground are described hereinafterin connection with an embodiment shown in the accompanying drawing in adiagrammatic form. The speedometer G consists of a frame l, which issuspended by means of the two pivots 2 and 2 10 in the two supports 3and 3", arranged transversely with respect to the direction of thelongitudinal axis of the airplane indicated by the arrow P. The centerof gravity of the frame l withthe gyroscopes placed therein lies belowthe l5 suspension axis 2'-2", so that the device constitutes a'gyrd-pendulum. In the frame there are two gyroscopes rotating inopposite directions which possess the same couple but in oppositedirections and are so coupled with one another by means of toothedsegments 5' and 5" that their dedections will be equal in angular extentbut opposite in direction. vThe precession axes 6' and 6" mounted in thependulum frame i are arranged in parallel relation to the direction 25of ight, whereas the axes of rotation of both gyroscopes are vertical,so that both gyroscopes are sensitive to swings about the transverseaxis of the airplane. The gyroscopes are held in their zero position bysprings i attached to the preces- 3o sion axes thereof. On theprecession axis t" a magnet 8 is arranged to turn in unison with saidaxis and with the casing of the gyroscope 4", said magnet beingenergized in a manner wellknown in the art through the conductors 8', 35which energization is proportional to .the directional force acting onthe gyroscopes in view of the rotation of the earth. The distance of thecenter of gravity of the entire gym-pendulum from the suspension axis2'- on the one hand, 40 and the spring forces, on the other hand, arepreferably so balancedthat the gym-pendulum possesses an oscillationperiod corresponding approximately to that of a mathematical pendulum ofthe length of the radius of the earth, i. e., 45 amounting toapproximately ,84 minutes. The pendulum has then the property ofremaining vertical at all times, independently oi' any horizontalacceleration. Furthermore, the gyroscopes, which 'are not under theinfluence of the actual 50 rotation of the earth, indicate by theirdeection of precession the speed which the airplane has relative toground in the direction of the arrow P. 'I'he horizontal acceleratlonsto which. the pendulum is subjected cannot impair the vertical l pomtionand, therefore, can not cause the gyroapparatus to oscillate. I'Thespeed relative to ground attained by adjusting the elevator control orby varying the propelling force o! the airplane is, however, at onceproperly determined by a corresponding increased or decreased deectionof the gyroscope. The decrease of the deection oi' the gyroscope isbrought about by an electrolytic system s arranged on the precessionaxis C'. The main electrode of the system 8 is disposed on theprecession axis of the gyroscope l' and the counter-electrodes arrangedat both sides of the main electrode are secured to the casing o! theelectrolytic system, which casing is mounted on the pendulum frame I inany suitable manner (not shown) which permits said casing to be turnedabout its axis either by hand or, if desired, also by an electric remotetransfer system in accordance with the speed oi' ight relative to groundto be maintained at a constant value in such a manner that the mainelectrode disposed on the precession axis of the gyroscope will swingwith respect tothe counter-electrodes in accordance with the departuresci the speed of flight at that particular moment from the desired speedrelative to ground.

The twocurrents ilowing from the main electrode to thecounter-electrodes of the electrolytic system serve to energize thecoils, wound in opposite direction, of the armature of an electricpivoted magnet Il whose contact arm II is, consequently, deilectedopposite to the force of the springs I2 in accordance with thedeflections of the main electrode relatively to the counter-electrodes.The deflection ci the'contact arm I I corresponds, therefore, to thedeparture of the speed of flight at that particular moment from thedesired speed relative to ground. These deflections are transmitted bymeans of the link I I and the double lever I4 iulcrumed aitrll to thecontrol needle Il of a controlled valve. This valve consistssubstantially ci the cylinder I8 and of the piston I1 displaceabletherein. The piston I1 is designed as a` dierential piston havingsurfaces I1' and I1" of different areas. The pressure medium,forinstance oil, is supplied to the cylinder VIt through a pressureregulating valve I8 and the conduit Il. 2l denotes the dischargeconduit. 3`-

is well known the controlledl valve operates asi'ollows: If the controlneedle I5 moves, for

instance, in the downward direction it throttles at'first the passage2i, so that the pressure in the upper chamber increases and the pistonI1 moves, consequently, in the downward It, however, the needle Il movesin the upward direction the passage 2l is completely opened so thatapproximately the same pressure prevails at both sides of the passage2l. The oil then exerts pressure only against the lower piston surfaceI1" so that the piston moves in the upward direction until the needle Ilagain throttlesjthe of the control needle Il. ,Within the-piston passage2i to suchfan extent that forces acting on both surfaces I1' and I1"ofthe differential -piston or balanced. The piston will, therefore.Drtically follow the movements I1 a further piston Ila isslidlblyarrangedhichissecuredtothecontrol rod'tl. The piston Ila is heldin the central position shown in the drawing by springs 22'.

' Furthermore, the piston 23 of a damping cylinder 24 nlled with oil orthe like is arranged on the rod 22, the cylinder being provided with aby-pass conduit having arranged therein an adjustable throttling valveIl'. The movement of the piston lla depends upon the differential actionof the pressures acting thereon through the channels 2lb and llc. Thedistance traversed is proportional to the adjusting speed of the pistonI1. Since the latter moves, however, in proportion to the deection ofthe pivoted magnet Il the rod 22 is displaced in accordance with thedefiection of the contact arm of the said magnet and with the speed withwhich this contact arm deilects. 'I'his additional adjustment of thespeed in accordance with the departures from the desired speed relativeto ground has the purpose oi' damping the oscillations, which occur inthe regulating device in the neighborhood of the desired speed relativeto ground.

The precession deflection of the reversing indieating .gyroscope 21transmitted to the right hand end of the dierential lever 2l issuperposed on the above-mentioned two control magnitudes acting on theleft hand end of the diierential lever. The rotation axis 21' as wellasthe precession axis 21" perpendicular thereto lie in the position ofrest in a vertical plane determined by the direction 'of ilight.sequently, sensitive to swings about the transverse axis of the airplaneand detiects in accordance with the angular speed of the airplane swingsabout such transverse axis, since the arm 2B arranged on the precessionaxis is normally held in a central position by the springs 29. By meansof a rod ,30 and a lever 3|, the sum of all three control magnitudes istransmitted to the control valve I! for the servo-motor 33 adjusting theelevator 34. The servo-motor causes at the same time through thedlierential lever 3| the control valve 32 to return to its originalposition so that the deilectlon of the elevator is exactly proportionalto the displacement ot the rod 3l, i. e., proportional vto the sum ofthe abov'e-mentioned three control magnitudes.

The departures of the speed of flight relative to ground from thedesired speed adjusted or set on thel electrolytic casing lact upon theelevator control only within a predetermined range. The right hand endof the differential lever Il carries a hook 35 cooperating with a loop30 which is secured to the diaphragm 31 of a diierential manometercontrollable from a distance, for instance by being eonnected to a Pitotstatic air speed indicator 38 exposed to the relative wind.

The diaphragm 31 is preferably subjected byA sponding to the mean speedof the airplane. The

deflections o i the diaphragm 31 then correspond to the departures o!the speed ofthe relative wind at that particular moment from this meanrelstive speed of flight. If the speed. relative Yto ground owing to astrong wind diners considerably from the speed oi' the relative wind itwill beapparentthat whentherelativespeedotiiight increases or decreasesabove or below a certain amountthediaphragmadjtsthe lever I4,it beingassumed that thevdlrectional force of the mssnet Ilas I1isrelatively lThe above-described'devioe cooperates preferably with an automaticdevice (not shown) for 'stabililzingthealtitullieoftlleairplainewhichd|evice maybedesignedhiawelleknownmannersothatinthecaseotdeparhiresfromthealtitude to be maintained constant analtimeterwhichthepilotmsysetbyhandi'ortheparticular The gyroscope is,con-A comparedtothatoi'thediaphragm slums to the.

that the propelling driving motor of the propellers through a regulatingdevice with servo-motor in such-a manner force is increased if thealtitude drops below the predetermined value and is decreased if thealtitude rises above the predetermined value. In the case, in which thespeed of flight relative to ground lies below a predetermined constantvalue the speedometer G acts upon the control valve 32 through themagnet I0' and the controlled valve in such a manner that the controlstick is pushed forward.` TheV altimeter which now indicates an altitudebelow the predetermined value then influences the gas supply of thepropeller motor, thus increasing the tractive force tained the desiredaltitude. The tractive force of the motor will, therefore, be indirectlyincreased or decreased through the adjustment of the elevator andthrough the change of the altitude of the airplane caused thereby untilthe airplane has again attained the desired speed of flight relative toground. In this case extremely small changes of altitude willpractically occur, since both the device above-described for thestabilization of the speed and the device for stabilizing the altitudesensitively.

I claim as my invention:

l. In an aircraft, a device responsive to the Speed of the craft withrespect to the ground, speed-stabilizing mechanism, an operativeconnection from said device to said mechanism, and means responsive tothe speed of the craft with respect to the surrounding air, forinterrupting or establishing said operative connection.

2. In an aircraft, a device responsive to the speed of the craft withrespect to the ground, speed-stabilizingmechanism, an operativeconnection from said device to said mechanism,

which influence the driving gear operate veryA means responsive tothespeed of the craft withrespect to the surrounding air, and means,controlled by such first-mentioned means, for estab- Y, said operativeconnection only when .the-

speed of the craft with respect tothe surrounding air drops below apredetermined limit.

3. In an aircraft, an elevator, a device responsive to the speed of thecraft with respect to the ground, an operative connection from saiddevice to said elevator, and means responsive to the speed of the craftwith respect to the surrounding air, for interrupting or establishingsaid operative connection. f

4. In an aircraft, an elevator, a device responsive to the speed of thecraft with respect to the sroimd, an operative connection from saiddevice to said elevator, means responsive to the speed of the craft withrespect to the surround` ing air, and means, controlled by suchiirst-mentioned means, for establishing said Voperative connection onlywhen the speed of the craft with. respect to the surrounding air dropsbelow a predetermined limit.

5. An apparatus according to claim 1, in which a Pitot static air speedindicator is employed as the means responsive to the speed of the craftwith respect to the surrounding air.

6. In a propelled aircraft, a device responsive to the speed of 'thecraft with respect to the ground, a speed stabilizing mechanismcontrolled by said device, and means responsive to the altitude of thecraft for controlling the action o1' the until the airplane has againatf aircraft propeller sc as to counteract any variations in altitudethat might be due to the operation of said speed-stabilizing mechanism.

'7. In an aircraft, a gyroscopic device responsive to the speed of thecraft with respect to the ground, said device comprising a gyroscopesystem free from the effect of the earths rotation and mounted to swingabout a suspension axis, and a. speed-stabilizing mechanism controlledby said gyroscopic device.

8. In an aircraft, a gyroscopic device responsive to the speed of thecraft with respect to the ground, said device comprising a gyroscopesystem free from the eiiect of the earths rotation and mounted to swingabout a suspension axis, a speed-stabilizing mechanism operativelyconnected with and controlled by said gyroscopic device, and adjustablemeans in the connection between said gyroscopic'device and said bilizingmechanism to be stabilized.

9. In an aircraft, a gyroscopic device responsive to the speed of thecraft with respect -to the ground, said device comprising agyroscopesystem free from the effect of the earths rotation and mountedto swing about a suspension axis, a speed-stabilizing mechanismoperatively connected with and controlled by said gyroscopic device, andadjustable means in the connection between said syroscopic device andsaid speedstabilizing mechanism, said adjustable means including amagnetic transmission controlled by a precession axle of said gyroscopicsystemand adjustable for setting the desired speed to be controlled. Y

10. In an aircraft, a gyroscopic device responsive to the speed of theground, said device comprising a gyroscope system free from the effectof the earths rotation and mounted to swing about a suspension axis, aspeed-stabilizing mechanism, an operative connection from Saidsyroscopic device and said mechanism, said connection including amovable member, and means for controlling said member in response to thespeed at which the craft swings about its transverse axis.

11. In an aircraft, a sive to the speed of the craft with respect to theground, said device comprising a gyroscope system free from the effectof the earths and mounted to swing about a suspension axis, aspeed-stabilizing mechanism, an operative connection from saidgyroscopic device and said mechanism, said connection including amovable member, and a reversing indicating gyroscope connected with saidmember and controlling it' in response to the speed at which the craftswings about its transverse axis.

i2. In an aircraft having its p force controlled for maintaining adesired altitude, an elevator, a device responsive to the speed of thecraft with respect to the ground, an operative connection from saiddevice to said elevator for adjusting the altitude of the craft asrequired to stabilize the speed of thecraft.

13. In an aircraft, a device responsive to the speed of the craft withrespect to the ground and means, controlled by said device, forstabilizingv A speed-stafor setting the desired speed gyroscopic deviceresponrotation l craft with respect to the

